This invention relates to allylated amide compounds and adhesives prepared from those compounds.
Adhesive compositions, particularly conductive adhesives, are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses are the bonding of integrated circuit chips to lead frames or other substrates, and the bonding of circuit packages or assemblies to printed wire boards.
The requirements for conductive adhesives in electronic packaging are that they have good mechanical strength, curing properties that do not affect the component or the carrier, and thixotropic properties compatible with existing application equipment currently used in the industry.
Another important aspect of an adhesive bonding or interconnection technology is the ability to rework the bond. For single chip packaging involving high volume commodity products, a failed chip can be discarded without significant loss. However, it becomes expensive to discard multi-chip packages with only one failed chip; consequently, the ability to rework the failed chip would be a manufacturing advantage. Today, one of the primary thrusts within the semiconductor industry is to develop adhesives that will meet all the requirements for adhesive strength and flexibility, but that will also be reworkable.
Conventional adhesive technology uses low viscosity thermosetting organic materials, the most widely used being epoxy systems. In order to achieve the required mechanical performance, relatively high molecular weight thermoplastics would be the preferred compositions for adhesive materials. These materials, however, have high viscosity or even solid film form, which are drawbacks to the manufacturing process. Therefore, there is a need for new adhesives that are easily dispensable to conform with automated manufacturing processes and that are reworkable.
This invention relates to allylated amide compounds that can be used in curable compositions. Allylated in this context means that allyl moieties are bonded to the nitrogen of amide moieties.
In another embodiment, this invention is an adhesive composition for use in electronic devices that comprises one or more allylated amide compounds, a curing initiator, and optionally, one or more fillers. The composition optionally may also contain mono- or polyfunctional vinyl compounds.
In another embodiment, this invention is the cured adhesive that results from the just described curable adhesive composition.
In another embodiment, this invention is a electronic assembly comprising an electronic component bonded to a substrate with a cured adhesive composition prepared from a composition comprising one or more allylated amide compounds, a curing initiator, optionally one or more fillers, and optionally one or more mono- or polyfunctional vinyl compounds.
In another embodiment, this invention is a method for adhering an electronic component to a substrate with a cured adhesive prepared from a composition comprising one or more allylated amide compounds, a curing initiator, optionally one or more fillers, and optionally, one or more mono- or polyfunctional vinyl compounds, the method comprising applying the adhesive to the component or the substrate, contacting the component and the substrate, and curing the adhesive in situ.
The allylated amide compounds, and vinyl compounds, used in the adhesive compositions of this invention are curable compounds, meaning that they are capable of polymerization, with or without crosslinking. As used in this specification, to cure will mean to polymerize, with or without crosslinking. Cross-linking, as is understood in the art, is the attachment of two polymer chains by bridges of an element, a molecular group, or a compound, and in general will take place upon heating. As cross-linking density is increased, the properties of a material can be changed from thermoplastic to thermosetting.
It is possible to prepare polymers of a wide range of cross-link density by the judicious choice and amount of mono- or polyfunctional compounds. The greater proportion of polyfunctional compounds reacted, the greater the cross-link density. In order to provide thermoplastic properties, adhesive compositions are prepared from mono-functional compounds to limit the cross-link density. However, a minor amount of poly-functional compounds can be added to provide some cross-linking and strength to the composition, provided the amount of poly-functional compounds is limited to an amount that does not diminish the desired thermoplastic properties. Within these parameters, the strength and elasticity of individual adhesives can be tailored to a particular end-use application.
The cross-link density can also be controlled to give a wide range of glass transition temperatures in the cured adhesive to withstand subsequent processing and operation temperatures.
In those cases where it is necessary to rework the assembly, the electronic component can be pried off the substrate, and any residue adhesive can be heated until it softens and is easily removed.
In the inventive adhesive compositions, the allylated amide compounds, and vinyl compounds if used in combination with the allylated amide compounds, will be present in the curable package adhesive compositions in an amount from 2 to 98 weight percent based on the organic components present (excluding any fillers).
The adhesive compositions will further comprise at least one free-radical initiator, which is defined to be a chemical species that decomposes to a molecular fragment having one or more unpaired electrons, highly reactive and usually short-lived, which is capable of initiating a chemical reaction by means of a chain mechanism. The free-radical initiator will be present in an amount of 0.1 to 10 percent, preferably 0.1 to 3.0 percent, by weight of the allylated amide compound, or combination of both allylated amide and vinyl compounds (excluding any filler). The free radical curing mechanism gives a fast cure and provides the composition with a long shelf life before cure. Preferred free-radical initiators include peroxides, such as butyl peroctoates and dicumyl peroxide, and azo compounds, such as 2,2xe2x80x2-azobis(2-methyl-propanenitrile) and 2,2xe2x80x2-azobis(2-methyl-butanenitrile).
Alternatively, the adhesive compositions may contain a photoinitiator, such as is sold by Ciba Specialty Chemicals under the trademark Irgacure, in lieu of the free-radical initiator, and the curing process may then be initiated by UV radiation. The photoinitiator will be present in an amount of 0.1 to 10 percent, preferably 0.1 to 3.0 percent, by weight of the allylated amide compound, or combination of both allylated amide and vinyl compounds (excluding any filler). In some cases, both photoinitiation and free-radical initiation may be desirable. For example, the curing process can be started by UV irradiation, and in a later processing step, curing can be completed by the application of heat to accomplish a free-radical cure.
In general, these compositions will cure within a temperature range of 50xc2x0 to 250xc2x0 C., and curing will be effected within a length of time of less than one minute to four hours. As will be understood, the time and temperature curing profile for each adhesive composition will vary, and different compositions can be designed to provide the curing profile that will be suited to the particular industrial manufacturing process.
Ease of application, even when thermoplastic properties are desired for the adhesive, is achieved by using relatively low molecular weight reactive oligomers or pre-polymers and curing these in situ after application to the electronic component or substrate. Applying the materials in an uncured state gives high processibility, and the resultant cured thermoplastic adhesive provides high mechanical performance.
Suitable conductive fillers for the adhesives are silver, copper, gold, palladium, platinum.
The allylated amide compounds suitable for use in the compositions of this invention have a structure represented by the formulas A and B as depicted here: 
As used throughout this specification, the notation C(O) refers to a carbonyl group. For these specific formulae, when lower case xe2x80x9cnxe2x80x9d is the integer 1, the compound will be a mono-functional compound; and when lower case xe2x80x9cnxe2x80x9d is an integer 2 to 6, the compound will be a poly-functional compound.
Formula A represents those compounds in which:
R9 is H, an alkyl or alkyleneoxy group having 1 to 18 carbon atoms, allyl, aryl, or substituted aryl having the structure 
in which R10, R11, and R12 are independently H or an alkyl or alkyleneoxy group having 1 to 18 carbon atoms;
each X independently is an aromatic group selected from the aromatic groups having the structures (I) through (V): 
and Q is a linear or branched chain alkyl, alkyloxy, alkyl amine, alkyl sulfide, alkylene, alkyleneoxy, alkylene amine, alkylene sulfide, aryl, aryloxy, or aryl sulfide species having up to about 100 atoms in the chain, which may contain saturated or unsaturated cyclic or heterocyclic substituents pendant from the chain or as part of the backbone in the chain, and in which any heteroatom present may or may not be directly attached to X;
or Q is a urethane having the structure: 
in which each R2 independently is an alkyl, aryl, or arylalkyl group having 1 to 18 carbon atoms; R3 is an alkyl or alkyloxy chain having up to 100 atoms in the chain, which chain may contain aryl substituents; X is O, S, N, or P; and v is 0 to 50;
or Q is an ester having the structure: 
in which R3 is an alkyl or alkyloxy chain having up to 100 atoms in the chain, which chain may contain aryl substituents;
or Q is a siloxane having the structure: (CR12)exe2x80x94[SiR4xe2x80x94O]fxe2x80x94SiR42xe2x80x94(CR12)gxe2x80x94 in which the R1 substituent independently for each position is H or an alkyl group having 1 to 5 carbon atoms and the R4 substituent independently for each position is an alkyl group having 1 to 5 carbon atoms or an aryl group, and e and g are independently 1 to 10 and f is 1 to 50; and
m is 0 or 1, and n is 1 to 6.
Formula B represents those compounds in which
R9 is H, or an alkyl or alkyleneoxy group having 1 to 18 carbon atoms, or an allyl group, or an aryl or substituted aryl having the structure 
in which R10, R11, and R12 are independently H or an alkyl or alkyleneoxy group having 1 to 18 carbon atoms;
Z is a linear or branched chain alkyl, alkyloxy, alkyl amine, alkyl sulfide, alkylene, alkyleneoxy, alkylene amine, alkylene sulfide, aryl, aryloxy, or aryl sulfide species having up to about 100 atoms in the chain, which may contain saturated or unsaturated cyclic or heterocyclic substituents pendant from the chain or as part of the backbone in the chain, and in which any heteroatom present may or may not be directly attached to K;
or Z is a urethane having the structure: 
in which each R2 independently is an alkyl, aryl, or arylalkyl group having 1 to 18 carbon atoms; R3 is an alkyl or alkyloxy chain having up to 100 atoms in the chain, which chain may contain aryl substituents; X is O, S, N, or P; and v is 0 to 50;
or Z is an ester having the structure: 
in which R3 is an alkyl or alkyloxy chain having up to 100 atoms in the chain, which chain may contain aryl substituents;
or Z is a siloxane having the structure:
xe2x80x94(CR12)exe2x80x94[(SiR42xe2x80x94O]fxe2x80x94SiR42xe2x80x94(CR1 2)gxe2x80x94 in which the R1 substituent independently for each position is H or an alkyl group having 1 to 5 carbon atoms and the R4 substituent independently for each position is an alkyl group having 1 to 5 carbon atoms or an aryl group, and e and g are independently 1 to 10 and f is 1 to 50;
K is an aromatic group selected from the aromatic groups having the structures (VI) through (XIII) (although only one bond may be shown to represent connection to the aromatic group K, this will be deemed to represent any number of additional bonds as described and defined by n): 
in which p is 1 to 100; 
in which p is 1 to 100; 
in which R5, R6, and R7 are a linear or branched chain alkyl alkyloxy, alkyl amine, alkyl sulfide, alkylene, alkyleneoxy, alkylene amine, alkylene sulfide, aryl, aryloxy, or aryl sulfide species having up to about 100 atoms in the chain, which may contain saturated or unsaturated cyclic or heterocyclic substituents pendant from the chain or as part of the backbone in the chain, and in which any heteroatom present may or may not be directly attached to the aromatic ring; or R5, R6, and R7 are a siloxane having the structure xe2x80x94(CR12)exe2x80x94[SiR42xe2x80x94O]fxe2x80x94SiR4 2xe2x80x94(CH3)gxe2x80x94 in which the R1 substituent is H or an alkyl group having 1 to 5 carbon atoms and the R4 substituent independently for each position is an alkyl group having 1 to 5 carbon atoms or an aryl group, and e is 1 to 10 and f is 1 to 50; 
and m is 0 or 1 and n is 1 to 6.
The compounds suitable for use in the adhesive compositions of this invention have a structure represented by one of the formulae:
xe2x80x83[Mxe2x80x94Xm]nxe2x80x94Q or [Mxe2x80x94Zm]nxe2x80x94K,
in which m is 0 or 1, and n is 1 to 6.
M represents a vinyl group and can be the maleimide moiety having the structure: 
in which R1 is H or C1 to C5 alkyl; or or the vinyl moiety having the structure: 
in which R1 and R2 are H or an alkyl having 1 to 5 carbon atoms, or together form a 5 to 9 membered ring with the carbons forming the vinyl group; B is C, S, N, O, C(O), Oxe2x80x94C(O), C(O)xe2x80x94O, C(O)NH or C(O)N(R8), in which R8 is C1 to C5 alkyl. Preferably, B is O, C(O), Oxe2x80x94C(O), C(O)xe2x80x94O, C(O)NH or C(O)N(R8); more preferably B is O, C(O), or C(O)N(R8).
X independently is an aromatic group selected from the aromatic groups having the structures (I) through (V): 
Preferably, X is structure (II), (III), (IV) or (V), and more preferably is structure (II).
Q and Z independently can be a linear or branched chain alkyl, alkyloxy, alkyl amine, alkyl sulfide, alkylene, alkyleneoxy, alkylene amine, alkylene sulfide, aryl, aryloxy, or aryl sulfide species having up to about 100 atoms in the chain, which may contain saturated or unsaturated cyclic or heterocyclic substituents pendant from the chain or as part of the backbone in the chain, and in which any heteroatom present may or may not be directly attached to X;
or Q and Z independently can be a urethane having the structure: 
in which each R2 independently is an alkyl, aryl, or arylalkyl group having 1 to 18 carbon atoms; R3 is an alkyl or alkyloxy chain having up to 100 atoms in the chain, which chain may contain aryl substituents; X is O, S, N, or P; and v is 0 to 50;
or Q and Z independently can be an ester having the structure: 
in which R3 is an alkyl or alkyloxy chain having up to 100 atoms in the chain, which chain may contain aryl substituents;
or Q and Z independently can be a siloxane having the structure: xe2x80x94(CR12)exe2x80x94[SiR4xe2x80x94O]fxe2x80x94SiR42xe2x80x94(CR12)gxe2x80x94 in which the R1 substituent independently for each position is H or an alkyl group having 1 to 5 carbon atoms and the R4 substituent independently for each position is an alkyl group having 1 to 5 carbon atoms or an aryl group, and e and g are independently 1 to 10 and f is 1 to 50.
Preferably, Q and Z will be a linear or branched chain alkyl, alkyloxy, alkylene, or alkyleneoxy species having up to about 100 atoms in the chain, as described with pendant saturated or unsaturated cyclic or heterocyclic substituents, or a siloxane as described, and more preferably is a linear or branched chain alkyl species or siloxane, as described.
K is an aromatic group selected from the aromatic groups having the structures (VI) through (XIII) (although only one bond may be shown to represent connection to the aromatic group K, this will be deemed to represent any number of additional bonds as described and defined by n): 
in which p is 1 to 100; 
in which p is 1 to 100; 
in which R5, R6, and R7 are a linear or branched chain alkyl, alkyloxy, alkyl amine, alkyl sulfide, alkylene, alkyleneoxy, alkylene amine, alkylene sulfide, aryl, aryloxy, or aryl sulfide species having up to about 100 atoms in the chain, which may contain saturated or unsaturated cyclic or heterocyclic substituents pendant from the chain or as part of the backbone in the chain, and in which any heteroatorn present may or may not be directly attached to the aromatic ring; or R5, R6, and R7 are a siloxane having the structure xe2x80x94(CR12)exe2x80x94[SiR42xe2x80x94O]fxe2x80x94SiR42xe2x80x94(CH3)gxe2x80x94 in which the R1 substituent is H or an alkyl group having 1 to 5 carbon atoms and the R4 substituent independently for each position is an alkyl group having 1 to 5 carbon atoms or an aryl group, and e is 1 to 10 and f is 1 to 50; 
Preferably, K is structure (VIII), (X) or (XI), more preferably is structure (X) or (XI), and most preferably is structure (X).
Depending on the nature of the substrate, the composition may also contain a coupling agent. A coupling agent as used herein is a chemical species containing a polymerizable functional group for reaction with the maleimide and other vinyl compound, and a functional group capable of condensing with metal hydroxides present on the surface of the substrate. Such coupling agents and the preferred amounts for use in compositions for particular substrates are known in the art. Suitable coupling agents are silanes, silicate esters, metal acrylates or methacrylates, titanates, and compounds containing a chelating ligand, such as phosphine, mercaptan, and acetoacetate. When present, coupling agents typically will be in amounts up to 10 percent by weight, and preferably in amounts of 0.1 to 3.0 percent by weight, of the allylated armide and vinyl compound, if any.
In addition, the compositions may contain compounds that lend additional flexibility and toughness to the resultant cured composition. Such compounds may be any thermoset or thermoplastic material having a Tg of 50xc2x0 C. or less, and typically will be a polymeric material characterized by free rotation about the chemical bonds, such as can be obtained by the presence of carbon-carbon double bonds adjacent to carbon-carbon single bonds, the presence of ester and ether groups, and the absence of ring structures. Suitable such modifiers include polyacrylates, poly(butadiene), polyTHF (polymerized tetrahydrofuran), CTBN (carboxy-terminated butyronitrile) rubber, and polypropylene glycol. When present, toughening compounds may be in an amount up to about 15 percent by weight of the maleimide and other monofunctional vinyl compound.
Siloxanes may also be added to the compositions to impart elastomeric properties. Suitable siloxanes are the methacryloxypropyl-terminated polydimethyl siloxanes, and the aminopropyl-terminated polydimethylsiloxanes, available from United Chemical Technologies.
The composition may also contain organic fillers, such as, polymers to adjust rheology. Other additives known and used in the art may also be used for specific purposes, such as, adhesion promoters. The selection of the types and amounts suitable is within the expertise of one skilled in the art.